The present invention relates to polyurethane foams having reduced resiliency, i.e. foams of the invention when compressed return to their original shape; however, the return process takes place slowly. This property of reduced resiliency enables the foams to be used in shock-absorbing and cushioning applications where it is desirable to stop a moving object without rebound or bouncing. The foams are also suitable for other applications such as earplugs, tampons, and packaging where it is necessary to compress the foam into a small size and, once compression is removed, it is desired for the foam to return slowly to its original size. The pressure exerted by the foam to return to its original size is desirable in that the pressure tends to hold the foam in place. Many conventional polyurethane foams regain their original size after compression within a fraction of a second. Foams of the invention take considerably longer.
Latices have been employed in combination with polyurethane precursors in preparing polyurethane foams. For example, U.S. Pat. No. 3,755,211 describes a foam formed by reacting a polyhydroxy compound with an organic polyisocyanate, water and a latex. Up to 20 parts of latex can be employed based on the weight of the polyhydroxy compound.
U.S. Pat. No. 2,933,013 describes both one-shot and prepolymer processes wherein a latex is mixed with a prepolymer with the water portion of the latex reacting with the NCO groups of the prepolymer to provide foaming. The latex may be employed at levels up to 10% based on the weight of the prepolymer. The resulting foams are said to have improved resilience and load bearing.
U.S. Pat. No. 3,582,499 describes a process wherein a synthetic polymer latex is foamed in the presence of a polyisocyanate which serves to crosslink the latex particles to improve physical properties of the resulting foam. The polyisocyanate (e.g. reduced methylene diisocyanate) is added during the foaming cycle and reacts with active hydrogen groups contained on the latex particles.